Intraocular lens alignment

ABSTRACT

A method for generating a radial alignment guide for an eye includes collecting preoperative alignment data relative to a pupil from an eye that is not dilated. The method also includes locating a pupil center of the eye while dilated. The method further includes displaying the alignment data on an image of the dilated eye relative to the pupil center. In particular embodiments, software embodied in a computer-readable medium is executable by a processor to perform the steps of such a method.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to provisionalapplication Ser. No. 61/153,709, filed Feb. 19, 2009, and provisionalapplication Ser. No. 61/155,562, filed Feb. 26, 2009.

BACKGROUND

For the past decade, ophthalmic surgeons have tried several methods tocorrect preexisting astigmatism during cataract eye surgery, includingmaking incisions into the cornea to alter the shape of the eye. Now dueto the unique design of toric intraocular lenses (IOL), astigmatism canbe reduced or corrected without further surgical intervention. A tonicIOL restores focus to the eye when the natural lens or cataract isremoved, but it is also designed to correct preexisting astigmatismusing the same technology that has been successfully used in contactlenses.

Before the surgery, the amount of corneal astigmatism that needs to becorrected must be determined. In general, the procedure is as follows:

-   -   1. Pre-Operative Examination (Keratometry, Corneal Topography,        Slit Lamp)    -   2. Calculation of IOL orientation    -   3. IOL Selection    -   4. Surgical insertion of toric IOL and alignment according to        pre-calculated axis

The success of such procedures depends in part upon the angular accuracyof the IOL alignment. All of the above steps have the potential tointroduce a certain degree of error resulting in under-correction ofastigmatism. However, a dominant source of error is the misalignment ofthe toric IOL according to the calculated angular value after it isinserted into the anterior chamber of a patient's eye during thecataract procedure. This may be, for example, due to the fact that thecalculated IOL angle is based on measurements conducted with the patientsitting upright (pre-op setup) and alert, while during surgery thepatient is in the supine position where cyclorotation occurs and underthe influence of local anesthetic. Each degree of angular error maycause a 3.3% loss of astigmatic correction by the toric IOL. Thus 10° oferror may cause a 33% reduction in the effect of the toric IOL, which isequivalent to using a spherical lens without astigmatism correction.

In order to avoid error due to the cyclorotation effect, there arecurrently several techniques to mark the eye with the meridian andpre-calculated IOL axis of alignment during the pre-operativeexamination. These techniques typically require the surgeon to placereference marks at the 3-o'clock and 9-o'clock meridians at the limbusutilizing markers or puncturing devices. Markings made by markers may beinaccurate, and may wash away or drift. Furthermore, puncturing thecornea is invasive and carries considerable risk of infection and/orother side effects.

SUMMARY

In certain embodiments of the present invention, a method for generatinga radial alignment guide for an eye includes collecting preoperativealignment data relative to a pupil from an eye that is not dilated. Themethod also includes locating a pupil center of the eye while dilated.The method further includes displaying the alignment data on an image ofthe dilated eye relative to the pupil center. In particular embodiments,software embodied in a computer-readable medium is executable by aprocessor to perform the steps of such a method.

In other embodiments, a system for generating a radial alignment guidefor an eye includes a memory, a processor, and a display. The memory isoperable to store preoperative alignment data relative to a pupil froman eye that is not dilated. The processor is operable to locate a pupilcenter of the eye while dilated. The display is operable to display thealignment data on an image of the dilated eye relative to the pupilcenter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be understood with reference to the followingdrawings wherein:

FIG. 1 shows an image of an eye with a radial overlay according to aparticular embodiment of the present invention.

FIG. 2 shows an alternative configuration for a radial grid overlay,along with user-provided radial measurements, according to anotherembodiment of the present invention.

FIG. 3 shows an alternative configuration for a radial grid overlay,along with user-provided radial measurements according to anotherembodiment of the present invention.

FIG. 4 is a block diagram of a surgical system according to a particularembodiment of the present invention.

FIG. 5 is a flow chart illustrating an example method of generating asurgical display according to a particular embodiment of the presentinvention.

DETAILED DESCRIPTION

In various embodiments of the present invention, toric intraocular lensalignment (IOL) for cataract surgery is improved by providing anaccurate radial grid or alignment guide to assist a surgeon in lensplacement. A slit lamp microscope may be used to obtain images of aneye, and an image overlay including a radial grid, lens alignment guide,and/or other fiducials for rotational alignment may be provided as asurgical guide in any suitable form including a computer display, aprinted image of the eye showing information, or by direct projectiononto the eye during the procedure

According to various methods and systems described herein, a radial gridis centered on a center of the pupil and overlaid on an image of the eye(or in one embodiment directly onto the eye). The pupil center may belocated, e.g., automatically using any appropriate center-finding imageprocessing technique, or manually through a point-and-click computerinterface or the like. For example, the pupil center can be locatedusing a variety of image analysis techniques, including but not limitedto the techniques described in U.S. Pat. No. 5,740,803 to Gray et al.,which is incorporated herein by reference. The grid may include verticaland horizontal meridians and a scale at any suitable degree of accuracy.Within a user interface, angular measurements may be selected and markedon the grid to various features of the eye such as blood vessels, irisfeatures, or any other appropriate fiducials. The grid may also includean alignment guide showing the correct rotational orientation for an IOLlens, as calculated prior to a surgical procedure. By calculating anangle relative to, e.g., the vertical meridian, an accurate guide may bedisplayed in the radial grid for use by a surgeon.

FIG. 1 shows an image of an eye with a radial overlay. As depicted, ahorizontal meridian passes through 0 degrees and 180 degrees, and avertical meridian passes through plus and minus 90 degrees. An angle of82.5 degrees has been marked as a reference angle to some eye featureselected by a surgeon or the like, and an angle of 156 degrees isdepicted for use in aligning a toric intraocular lens (also referred togenerally herein as a lens.

Other aspects of systems and methods for aligning a lens are describedbelow. In an embodiment using a slit lamp microscope, a suitable videocamera may be mounted on a slit lamp microscope through a beam splitter.The camera may be connected to a computer with image acquisitionhardware using a connector such as USB, FireWire or GigE port. Livedisplay may be started, and the camera may be aligned so that thehorizontal axis of the camera's field of view is aligned with thehorizontal slit of the slit lamp. High quality images may be capturedwith the patient sitting upright, and software may attempt toautomatically locate the central point of the pupil. The software mayalso include a manual pupil localization tool. Once the central point ofthe pupil is defined, the software may overlay a radial grid with itscenter located on that point as shown, e.g., in FIG. 1. The 0 to 180°axis of the radial will coincide with the 3- and 9-o'clock meridians ofthe eye since the camera is rotationally calibrated with the slit lamp.The software may also have the capability to provide the following:

-   -   Overlay of the toric IOL axis according to the angular value        calculated through Keratometry. The toric axis IOL axis will        cross the center of the dial and the angular value will be in        reference to the 0 to 180° axis of the overlaid dial (see line        with angle value 156 degrees in FIG. 1)    -   Overlay of axes that cross through the dial center and other        anatomical landmarks that the surgeon chooses as fiducial marks        on the eye's iris periphery or limbar vessels. The software will        display the angular value next to each one of these reference        points (see line with angle value 82.5 degrees in FIG. 1).

The software may also designate the images with the left or right eyedesignation and temporal or nasal side of the eye (see letters “R” and“T” in FIG. 1)

The processed images may be stored on the computer's hard drive,removable memory, or in the patient database of the medical facility.The surgeon may retrieve and display images with overlay in an operatingroom in a high quality photograph or on a monitor, or the overlay may beprojected directly onto a patient's eye using an appropriate projector.

Based on the overlaid axes of the fiducial points, the surgeon canaccurately place a surgical protractor that determines toric IOLinsertion regardless of the cyclorotation effect. As soon as theprotractor is aligned with the actual eye meridians, the surgeon canproceed with aligning the toric IOL according to the calculated angularvalue. FIGS. 2 and 3 illustrate alternative arrangements for a radialoverlay, along with user-provide measurements and/or lens alignmentinformation.

This method addresses several sources of error in the IOL alignmentprocess for cataract surgery by

-   -   a. Providing a mechanism for accurate camera alignment with the        slit lamp microscope    -   b. Offering precise location of the pupil center based on image        analysis    -   c. Enabling accurate protractor placement during surgery by        guiding the surgeon to place the protractor according to the        actual meridians of the eye hence generating an accurate        reference angular system

The methods or processes described above, and steps thereof, may berealized in hardware, software, or any combination of these suitable fora particular application. FIG. 4 is a block diagram of a system 100 forgenerating a surgical display according to a particular embodiment ofthe present invention. The system 100 includes a console 102 having aprocessor 104. The processor 104 may be one or more microprocessors,microcontrollers, embedded microcontrollers, programmable digital signalprocessors or other programmable device, along with internal and/orexternal memory 106. The processor 104 may also, or instead, be embodiedin an application specific integrated circuit, a programmable gatearray, programmable array logic, or any other device or combination ofdevices that may be configured to process electronic signals. The memory106 may be any suitable form of data storage, including electronic,magnetic, or optical memory, whether volatile or non-volatile, thatincludes code 108 comprising instructions executed by processor 104. Itwill further be appreciated that computer executable code 108 may becreated using a structured programming language such as C, an objectoriented programming language such as C++, or any other high-level orlow-level programming language (including assembly languages, hardwaredescription languages, and database programming languages andtechnologies) that may be stored, compiled or interpreted to run on oneof the above devices, as well as heterogeneous combinations ofprocessors, processor architectures, or combinations of differenthardware and software.

In the embodiment depicted in FIG. 4, the system 100 also includes adisplay 108 and a microscope 110 for observing an eye during surgery.The display 108 may include any suitable output device for generating analignment guide for the eye, including a printer, a video display, or alight projector. In particular embodiments, the display 108 may becoupled to the microscope 110 so that the image is projected into theview of the microscope. The microscope 110 may be any suitable tool forvisually inspecting the eye, which may include electronic and/or opticalviews. Various other suitable components, including any of the examplesdescribed herein, may also be substituted for the components of system100.

FIG. 5 is a flow chart 200 illustrating an example method for generatinga surgical display including a radial alignment guide in accordance witha particular embodiment of the present invention. At step 202,preoperative alignment data relative to a pupil is collected from an eyethat is not dilated. At step 204, the eye is dilated. At step 206, thepupil center is located. The pupil center can be located manually, suchas by using a pointing device, or automatically, such as by imageanalysis software. At step 208, an alignment guide is displayed on animage of the dilated eye relative to the pupil center. The alignmentguide can correspond to any of the various embodiments described herein.

Thus, in one aspect, each method described above and combinationsthereof may be embodied in computer executable code that, when executingon one or more computing devices, performs the steps thereof. In anotheraspect, the methods may be embodied in systems that perform the stepsthereof, and may be distributed across devices in a number of ways, orall of the functionality may be integrated into a dedicated, standalonedevice or other hardware. In another aspect, means for performing thesteps associated with the processes described above may include any ofthe hardware and/or software described above. All such permutations andcombinations are intended to fall within the scope of the presentdisclosure.

While the invention has been disclosed in connection with the preferredembodiments shown and described in detail, various modifications andimprovements thereon will become readily apparent to those skilled inthe art.

What is claimed is:
 1. A method for generating a radial alignment guide for an eye, comprising: collecting preoperative rotational alignment data relative to a pupil from an eye that is not dilated, the preoperative rotational alignment data comprising a rotational offset relative to a meridian of the eye; locating a pupil center of the eye while dilated during implantation of a toric intraocular lens; displaying a radial grid on an intraoperative image of the dilated eye, the radial grid comprising a vertical axis and a horizontal axis each passing through the located pupil center; and displaying a rotational alignment axis for the toric intraocular lens, during the implantation of the toric intraocular lens, on the intraoperative image of the dilated eye, the rotational alignment axis being offset relative to one of the vertical axis and the horizontal axis by an amount equal to the rotational offset of the preoperative rotational alignment data.
 2. The method of claim 1, wherein locating the pupil center comprises manually moving a pointing device to locate a center of an eye.
 3. The method of claim 1, wherein locating the pupil center comprises automatically locating the pupil center using image analysis software.
 4. A system for generating a radial alignment guide for an eye, comprising: a memory operable to store preoperative rotational alignment data relative to a pupil from an eye that is not dilated, the preoperative rotational alignment data comprising a rotational offset relative to a meridian of the eye; a processor operable to locate a pupil center of the eye while dilated during implantation of a toric intraocular lens; and a display operable to display: a radial grid on an intraoperative image of the dilated eye, the radial grid comprising a vertical axis and a horizontal axis each passing through the located pupil center; and a rotational alignment axis for the toric intraocular lens, during the implantation of the toric intraocular lens, on an intraoperative image of the dilated eye, the rotational alignment axis being offset relative to one of the vertical axis and the horizontal axis by an amount equal to the rotational offset of the preoperative rotational alignment data.
 5. The system of claim 4, further comprising a pointing device that is manually movable to indicate a center of the pupil to the processor.
 6. The system of claim 4, wherein the processor is operable to locate the pupil center using image analysis software.
 7. Software embodied in a non-transitory computer-readable medium executable by a processor to perform the steps of: collecting preoperative rotational alignment data relative to a pupil from an eye that is not dilated, the preoperative rotational alignment data comprising a rotational offset relative to a meridian of the eye; locating a pupil center of the eye while dilated during implantation of a toric intraocular lens; displaying a radial grid on an intraoperative image of the dilated eye, the radial grid comprising a vertical axis and a horizontal axis each passing through the located pupil center; and displaying a rotational alignment axis for the toric intraocular lens, during the implantation of the toric intraocular lens, on the intraoperative image of the dilated eye, the rotational alignment axis being offset relative to one of the vertical axis and the horizontal axis by an amount equal to the rotational offset of the preoperative rotational alignment data.
 8. The software of claim 7, wherein locating the pupil center comprises receiving an indication of the center of the pupil from a pointing device.
 9. The software of claim 7, wherein locating the pupil center comprises automatically locating the pupil center using image analysis software. 